High-strength and high-toughness lamellar-tearing-resistant super-thick steel plate and manufacturing method thereof

Abstract

The invention relates to a high-strength and high-toughness lamellar-tearing-resistant extra-thick steel plate and a manufacturing method thereof. The steel plate comprises the following chemical components: C, Si, Mn, P, S, Als, Ti, Cu, Ni, Nb, V, Mg, B and the balance of Fe and inevitable impurities. Through the technical integration of low-carbon equivalent composition design, calcium-magnesium composite treatment and inclusion form control, continuous casting under heavy pressure and multi-directional rolling and three-stage gradient controlled cooling, under the premise of not depending on precious alloy elements such as Cr, Mo and Zr, the steel plate with the thickness of 80-150 mm, the yield strength of 460-550 MPa grade and the tensile strength of 460-550 MPa grade is stably produced, and the steel plate with the high tensile strength is obtained. The super-thick steel plate has excellent low-temperature toughness, excellent lamellar tearing resistance (the Z-direction reduction of area is larger than or equal to 40%) and good large heat input weldability, and the technical problems existing in the field for a long time are solved.

Description

Technical Field

[0001] This invention relates to the field of steel plate production technology, and in particular to a high-strength, high-toughness, anti-lamellar tearing extra-thick steel plate and its manufacturing method. Background Technology

[0002] As marine engineering, large-scale hydropower facilities, and super high-rise buildings develop towards deeper water, larger capacity, and super high-rise, respectively, their key structural nodes (such as offshore platform jacket nodes, large hydropower station pressure steel pipe nodes, and heavy column-beam nodes in super high-rise buildings) generally adopt ultra-thick steel plates with a thickness of ≥80mm, or even ≥150mm. This places unprecedentedly stringent requirements on the material's yield strength (≥460MPa), low-temperature toughness, and resistance to lamellar tearing (Z-axis performance). Traditional steel plate production technologies struggle to simultaneously meet these performance indicators, primarily due to the following bottlenecks: 1. The contradiction between high strength and excellent weldability is difficult to reconcile: In order to achieve high strength, it is usually necessary to increase the carbon equivalent (Ceq) and crack sensitivity index (Pcm), but this will directly lead to the deterioration of the weldability of the steel plate, high preheating temperature during welding, high sensitivity to cold cracking, complex construction and high cost.

[0003] 2. Internal defects caused by large thickness are difficult to eliminate: During the solidification process of extra-thick plate continuously cast billets, the central region cools slowly, which easily leads to severe central segregation (such as the aggregation of Mn, P, and S) and central porosity. These casting defects are difficult to completely weld together in subsequent rolling and will be inherited into the finished steel plate in the form of banded structures or lamellar inclusions. They become stress concentration sources and crack initiation sites when subjected to stress in the thickness direction (Z direction), resulting in low Z-direction reduction of area (Z%) and poor resistance to lamellar tearing.

[0004] 3. Traditional oxide metallurgy offers limited contribution to combating lamellar tearing: Existing oxide metallurgical technologies mainly focus on improving the transverse (parallel to the plate surface) toughness of the weld heat-affected zone (HAZ). Research on how to utilize dispersed particles to improve Z-axis properties and suppress lamellar tearing is insufficient, and the technical pathways are unclear. Conventional spheroidizing treatment is effective against sulfides, but its effect on controlling the morphology of hard inclusions such as alumina is poor.

[0005] 4. Severely uneven microstructure and properties in the thickness direction: During the rolling and cooling process of extra-thick plates, the deformation and cooling rate of the surface and the core are very different, resulting in a significant gradient in microstructure and properties. The phenomenon of "strong surface and weak core" often occurs, and the toughness of the core often becomes the shortcoming of the overall plate performance.

[0006] Furthermore, existing technologies typically employ methods such as adding expensive alloying elements (e.g., nickel, molybdenum, which incur high smelting costs) or sacrificing some strength to achieve Z-axis properties, but these methods have limited effectiveness and poor economic efficiency. Therefore, there is an urgent need to develop an innovative manufacturing technology that can systematically address the complex contradiction of "high strength, large thickness, excellent Z-axis properties, and good weldability." Summary of the Invention

[0007] This invention provides a high-strength, high-toughness, and anti-lamellar tearing extra-thick steel plate and its manufacturing method. Through the integration of technologies such as "low-carbon equivalent composition design", "calcium-magnesium composite treatment and inclusion morphology control", "continuous casting under heavy pressure and multi-directional rolling", and "three-stage gradient controlled cooling", it can stably produce extra-thick steel plates with a thickness of 80-150 mm, a yield strength of 460-550 MPa, excellent low-temperature toughness, outstanding anti-lamellar tearing performance (Z-direction reduction of area ≥40%), and good high heat input weldability without relying on precious alloying elements such as Cr, Mo, and Zr. This invention overcomes a long-standing technical problem in this field.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A high-strength, high-toughness, lamellar tear-resistant extra-thick steel plate, wherein the chemical composition of the steel, by weight percentage, is: C: 0.04%–0.07%, Si: 0.10%–0.25%, Mn: 1.40%–1.70%, P≤0.008%, S≤0.0015%, Als: 0.020%–0.035%, Ti: 0.012%–0.020%, Cu: 0.25%–0.50%, Ni: 0.20%–0.40%, Nb: 0.025%–0.045%, V: 0.04%–0.08%. %, Mg: 0.0012%~0.0020%, B: 0.0010%~0.0020%; balance is Fe and unavoidable impurities; carbon equivalent 0.28%≤Ceq≤0.47%, Ceq=C+Si / 24+Mn / 6+Ni / 40+Cr / 5+Mo / 4+V / 14; weld crack sensitivity index 0.1325%≤Pcm≤0.203%, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0009] The finished steel plate has a gradient structure that transitions from ultrafine bainite on the surface to acicular ferrite in the core.

[0010] A method for manufacturing a high-strength, high-toughness, lamellar tear-resistant extra-thick steel plate includes the following steps: 1) Converter smelting: The carbon content at the converter endpoint is controlled at 0.04% to 0.07%, and the tapping temperature is controlled at 1600℃ to 1630℃. Composite deoxidation and alloying are adopted during the tapping process to ensure that the steel composition meets the design requirements. 2) LF refining and calcium-magnesium composite treatment: The LF refining time is controlled at 30-45 min. In the later stage of refining, calcium-magnesium composite treatment is carried out, and the calcium-aluminum mass ratio Ca / Als is controlled within the range of 0.09-0.11. Finally, soft argon blowing is carried out for ≥15 min. 3) Continuous casting: Fully protected casting is adopted; the superheat of the tundish is 15-22℃, and the casting speed is 0.7-1.0m / min; the thickness of the continuously cast slab is ≥230mm, and heavy pressure is used at the end of solidification, with a total reduction of 15-22mm and a reduction rate of 0.8-1.0mm / s; the center segregation index of the slab is controlled to be ≤1.05. 4) Slab heating and multi-directional deformation rolling: The slab heating temperature is 1180~1220℃, and the holding time is calculated as 4~6 times the slab thickness. The slab thickness is in meters (m) and the holding time is in hours (h). The multi-directional deformation rolling process is adopted, as detailed below: Step 1: Recrystallization zone rolling, performing one pass of large-reduction vertical roll rolling on the center area of ​​the wide side of the slab, with the side pressure controlled at 25% to 35%; Step 2: Rolling in the non-recrystallization zone. Rotate the slab 90° and perform one transverse rolling pass, with the deformation controlled at 10% to 15%. Step 3: Complete the remaining deformation using conventional longitudinal rolling, with the final rolling temperature controlled at 810–850℃, and the cumulative total reduction rate ≥75%; 5) Three-stage gradient cooling: First stage: Rapidly cool the surface of the steel plate to 550-600℃ at a cooling rate of ≥25℃ / s; Second stage: Turn off the cooling water and air cool for 30-60 seconds; The third stage: Restart the cooling water and cool the steel plate as a whole to the target final cooling temperature of 450-480℃ at a cooling rate of 5-8℃ / s, and then air cool it to room temperature.

[0011] In step 2), during the calcium-magnesium composite treatment, magnesium wire is first fed in for magnesium treatment to control the Mg content in the steel within the target range; then calcium-iron wire is fed in for calcium treatment.

[0012] In step 2), the calcium-aluminum mass ratio Ca / Als is controlled within the range of 0.095 to 0.105.

[0013] In step 3), the solidification end of the continuously cast slab refers to the range of solid fraction of 0.7 to 0.9.

[0014] In step 4), the recrystallization zone rolling is carried out in a temperature range of ≥1050℃, and the non-recrystallization zone rolling is carried out in a temperature range of 850~900℃.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) Excellent and stable resistance to lamellar tearing: The 80-150mm thick steel plate produced according to the method of the present invention can stably reach 40%-50% in the Z direction of cross-sectional reduction (Z%), which is far higher than the requirements of relevant standards such as marine engineering (≥25%), and the performance fluctuation is small, which provides a fundamental guarantee for the safety of high-constraint welded joints.

[0016] (2) Perfect combination of high strength and high toughness: The yield strength of the finished steel plate is stable in the range of 460 to 550 MPa, while having excellent low-temperature toughness, with a transverse impact energy of ≥200 J at -40℃. After high heat input welding (300 to 400 kJ / cm), the impact energy of HAZ at -40℃ is ≥100 J, meeting the stringent requirements of high-end structures for the comprehensive performance of materials.

[0017] (3) Excellent weldability and convenient construction: Thanks to the low carbon equivalent design (Ceq≤0.42%, Pcm≤0.21%), the finished steel plate has extremely low sensitivity to cold cracking during welding. In actual construction, high heat input welding can be carried out with a lower preheating temperature (≤75℃) or even without preheating, which simplifies the process, improves efficiency, and reduces costs.

[0018] (4) Significantly improved uniformity of microstructure and properties in the thickness direction: By combining multi-directional rolling with gradient controlled cooling, the performance gradient in the thickness direction of the extra-thick plate is effectively improved. The difference in impact energy between the 1 / 4 section of the plate thickness and the core at -40℃ can be controlled within 20J, thus avoiding the core toughness becoming a weakness.

[0019] (5) The composition and process are economical and feasible: This invention does not rely on expensive alloying elements such as Cr, Mo, and Zr. The target performance is achieved through the rational application of Cu and Ni and the fine control of the whole process. It can be stably produced on existing mainstream metallurgical equipment and has excellent prospects for industrial promotion and market competitiveness.

[0020] (6) The product is highly targeted: it is especially suitable for key load-bearing parts such as marine platform nodes and heavy hydroelectric structures. Detailed Implementation

[0021] The present invention discloses a high-strength, high-toughness, lamellar tear-resistant extra-thick steel plate. The chemical composition of the steel, by weight percentage, is: C: 0.04%–0.07%, Si: 0.10%–0.25%, Mn: 1.40%–1.70%, P≤0.008%, S≤0.0015%, Als: 0.020%–0.035%, Ti: 0.012%–0.020%, Cu: 0.25%–0.50%. %, Ni: 0.20%~0.40%, Nb: 0.025%~0.045%, V: 0.04%~0.08%, Mg: 0.0012%~0.0020%, B: 0.0010%~0.0020%; balance is Fe and unavoidable impurities; carbon equivalent 0.28%≤Ceq≤0.47%, Ceq=C+Si / 24+Mn / 6+Ni / 40+Cr / 5+Mo / 4+V / 14; weld crack sensitivity index 0.1325%≤Pcm≤0.203%, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0022] The purpose of adding Cu and Ni to the chemical composition of the steel plate described in this invention is to improve strength through solid solution strengthening and improved low-temperature toughness without significantly increasing the carbon equivalent.

[0023] The present invention discloses a method for manufacturing a high-strength, high-toughness, lamellar-tear-resistant extra-thick steel plate, comprising the following steps: 1) Converter smelting: The carbon content at the converter endpoint is controlled at 0.04% to 0.07%, and the tapping temperature is controlled at 1600℃ to 1630℃. Composite deoxidation and alloying are adopted during the tapping process to ensure that the steel composition meets the design requirements. 3) LF refining and calcium-magnesium composite treatment: The LF refining time is controlled at 30-45 minutes for desulfurization, fine-tuning of composition, and precise temperature control. In the later stages of refining, a calcium-magnesium composite treatment is performed. First, magnesium wire is fed in for magnesium treatment, controlling the Mg content in the steel within the target range; then, calcium-iron wire is fed in for calcium treatment, precisely controlling the calcium-aluminum mass ratio (Ca / Als) within a narrow range of 0.09-0.11 (preferably within the range of 0.095-0.105).

[0024] This invention employs a calcium-magnesium composite treatment to partially modify high-melting-point Al2O3 (melting point approximately 2050℃) in steel into low-melting-point (melting point approximately 1500–1600℃) calcium aluminate, which then combines with numerous deoxidation products such as MgO and TiO2 to form a dispersed secondary phase with MgO and TiO2 as nucleation cores. The numerous dispersed secondary phases are easier to control in subsequent processing, maintaining a spherical or near-spherical shape (sphericity ≥ 0.7). Furthermore, the addition of magnesium refines the secondary phase size, making it less prone to excessive elongation into plates during rolling deformation. This significantly reduces the risk of it becoming a crack initiation point under Z-axis stress, a key measure for improving resistance to lamellar tearing. Soft argon blowing time ≥ 15 min aims to promote the full flotation of inclusions.

[0025] 3) Continuous casting: Full protective casting is employed. For continuously cast slabs with a thickness ≥230mm, heavy pressure is applied at the end of solidification (in the range of solid fraction 0.7–0.9), with a total reduction of 15–22mm and a reduction rate of 0.8–1.0mm / s. The center segregation index of the slab is controlled to ≤1.05. Simultaneously, the secondary cooling regime is optimized, with stronger cooling in the heavy pressure region. The superheat of the tundish is controlled to 15–22℃, and the casting speed is matched to the slab thickness, typically 0.7–1.0m / min.

[0026] This invention employs a combination of heavy pressure and forced cooling to apply immense pressure to the semi-solidified core of the slab, forcibly squeezing the solute-rich liquid metal between dendrites. This forces the molten metal to flow in the opposite direction to the already solidified leading edge and be diluted, thereby significantly reducing or even eliminating center segregation and V-shaped segregation. The goal is to control the slab's center segregation index below 1.05. Simultaneously, the powerful reducing force effectively welds together center shrinkage cavities and porosity, achieving densification of the slab core and laying a solid foundation for obtaining high Z-axis performance.

[0027] 4) Slab heating and multi-directional deformation rolling: The slab heating temperature is 1180~1220℃, and the holding time is calculated as 4~6 times the slab thickness (slab thickness is in m, holding time is in h) to ensure sufficient and uniform heating.

[0028] The multi-directional deformation rolling process, known as "1+1+N", is adopted, as follows: Step 1 (i.e. the first "1", using vertical roll large reduction): recrystallization zone rolling (≥1050℃), one large reduction vertical roll rolling is carried out on the central area of ​​the wide side of the slab, and the side pressure is controlled at 25% to 35%; it is used to initially break up the coarse columnar crystals and improve the deformation permeability in the thickness direction.

[0029] The second step (i.e. the second "1") adopts reversible rolling: rolling in the non-recrystallization zone (temperature range of 850℃~900℃), rotating the slab 90° to carry out one transverse rolling, with the deformation controlled at 10%~15%; the aim is to disrupt the distribution of banded structures and inclusions formed along the rolling direction and improve anisotropy.

[0030] The third step (i.e. "N") is to complete the remaining deformation by conventional longitudinal rolling, with the final rolling temperature controlled at 810-850℃ and the cumulative total reduction rate ≥75%; to ensure that the deformation fully penetrates into the core of the slab and achieves grain refinement across the entire thickness range.

[0031] 5) Immediately after rolling, the material enters an accelerated cooling (ACC) unit for three-stage gradient controlled cooling: The first stage (Ultra-Fast Cooling UFC): The surface of the steel plate is rapidly cooled to 550-600℃ at a cooling rate of ≥25℃ / s (at which point the core temperature of the steel plate is about 650-700℃), which aims to suppress the precipitation of proeutectoid ferrite on the surface of the steel plate and obtain a high-strength ultrafine bainitic structure.

[0032] Second stage (temperature homogenization): Turn off the cooling water and air cool for 30-60 seconds; reduce the temperature gradient in the thickness direction of the steel plate and make it more uniform.

[0033] The third stage (Accelerated Cooling, ACC): The cooling water is restarted, and the steel plate is cooled to the target final cooling temperature of 450–480°C at a relatively slow cooling rate of 5–8°C / s, followed by air cooling to room temperature. This cooling rate allows sufficient time for phase transformation to occur in the core of the steel plate, forming a multiphase structure dominated by high-toughness acicular ferrite and containing a small amount of granular bainite. Ultimately, an optimized gradient microstructure of "superfine bainite on the surface (high strength) + acicular ferrite in the core (high toughness)" is obtained, achieving a reasonable match between strength and toughness in the thickness direction.

[0034] The finished steel plate has a gradient structure that transitions from ultrafine bainite on the surface to acicular ferrite in the core.

[0035] Unless otherwise specified, all contents in this invention are mass contents.

[0036] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0037]

Example 1

[0038] The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.05%, Si: 0.18%, Mn: 1.55%, P: 0.007%, S: 0.0012%, Als: 0.028%, Ti: 0.015%, Cu: 0.35%, Ni: 0.30%, Nb: 0.035%, V: 0.06%, Mg: 0.0018%, B: 0.0015%, Ceq=0.3234%, Pcm=0.1629%.

[0039] The steel plate manufacturing process in this embodiment is as follows: 1. Converter smelting and LF refining: The final C content in the converter is 0.05%, and the tapping temperature is 1615℃. The LF refining time is 38 min, and after calcium-magnesium composite treatment, the [Ca] / [Als] ratio is controlled to be 0.10. Soft argon blowing is performed for 18 min.

[0040] 2. Continuous casting: Slab thickness 230mm, tundish superheat 18℃, casting speed 0.85m / min. Heavy reduction was used at the end of slab solidification, with a total reduction of 18mm, and the center segregation index was measured to be 1.03.

[0041] 3. Rolling: The slab is heated to 1200℃ and held for 66 minutes. A multi-directional deformation rolling process is adopted. In the first step of rolling in the recrystallization zone, the side pressure of the vertical roll is 30%. In the second step of rolling in the non-recrystallization zone, the reversing rolling deformation rate is 12%. The remaining deformation is completed in the third step. The final rolling temperature is 830℃, and the cumulative total reduction rate is 78%.

[0042] 4. Three-stage gradient cooling: The first stage rapidly cools the steel plate surface to 580°C at a cooling rate of 28°C / s; the second stage air-cools for 40 seconds; the third stage cools the entire steel plate to 460°C at a cooling rate of 7°C / s; and finally, air-cools to room temperature.

[0043] The performance test results of the steel plate produced in this embodiment are as follows: Mechanical properties: Yield strength 475MPa, tensile strength 590MPa, elongation 24%.

[0044] Low temperature toughness: 235J (average) transverse impact energy at -40℃, 82J (Z-direction) impact energy in the thickness direction at -40℃.

[0045] Z-direction performance: Z-direction reduction of area 45%.

[0046] Welding performance: After welding thermal simulation with a heat input of 400 kJ / cm, the impact energy of HAZ at -40℃ is 108 J.

[0047] Metallographic structure: The surface layer is ultrafine bainite, and the core is acicular ferrite. The original austenite grain size is 12 μm on the surface and 18 μm in the core.

[0048]

Example 2

[0049] The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.06%, Si: 0.20%, Mn: 1.65%, P: 0.006%, S: 0.0010%, Als: 0.032%, Ti: 0.018%, Cu: 0.45%, Ni: 0.35%, Nb: 0.040%, V: 0.07%, Mg: 0.0016%, B: 0.0018%, Ceq=0.357%, Pcm=0.1848%.

[0050] The steel plate manufacturing process in this embodiment is as follows: 1. Converter smelting and LF refining: The final C content in the converter is 0.06%, and the tapping temperature is 1620℃. The LF refining time is 40 min, and after calcium-magnesium composite treatment, the [Ca] / [Als] ratio is controlled to be 0.098. Soft argon blowing is performed for 20 min.

[0051] 2. Continuous casting: Tundish superheat 20℃, casting speed 0.80m / min. Slab thickness 230mm, heavy reduction at the end of slab solidification, total reduction 20mm, the center segregation index was measured to be 1.02.

[0052] 3. Rolling: The slab is heated to 1210℃ and held for 68 minutes. A multi-directional deformation rolling process is adopted. In the first step of rolling in the recrystallization zone, the side pressure of the vertical roll is 28%. In the second step of rolling in the non-recrystallization zone, the reversing rolling deformation rate is 14%. The remaining deformation is completed in the third step. The final rolling temperature is 820℃, and the cumulative total reduction rate is 76%.

[0053] 4. Three-stage gradient cooling: The first stage rapidly cools the steel plate surface to 570°C at a cooling rate of 30°C / s; the second stage air-cools for 45 seconds; the third stage cools the entire steel plate to 470°C at a cooling rate of 6°C / s; and finally, air-cools to room temperature.

[0054] The performance test results of the steel plate produced in this embodiment are as follows: Mechanical properties: Yield strength 515MPa, tensile strength 635MPa, elongation 22%.

[0055] Low temperature toughness: Transverse impact energy at -40℃ is 210J (average value), and thickness direction (Z direction) impact energy at -40℃ is 75J.

[0056] Z-direction performance: Z-direction reduction of area 42%.

[0057] Welding performance: After welding thermal simulation with a heat input of 350 kJ / cm, the impact energy of HAZ at -40℃ is 115 J.

[0058] Inclusion analysis: Scanning electron microscopy showed that most of the composite secondary phases were spherical or nearly spherical, with an average size of 0.4 μm.

[0059]

Example 3

[0060] The chemical composition of the steel plate, by weight percentage, is as follows: C: 0.065%, Si: 0.22%, Mn: 1.70%, P: 0.005%, S: 0.0009%, Als: 0.030%, Ti: 0.017%, Cu: 0.50%, Ni: 0.40%, Nb: 0.045%, V: 0.075%, Mg: 0.0019%, B: 0.0016%, Ceq=0.3726%, Pcm=0.1965%.

[0061] The steel plate manufacturing process in this embodiment is as follows: 1. Converter smelting and LF refining: The final C content in the converter is 0.065%, and the tapping temperature is 1625℃. The LF refining time is 45 min, and after calcium-magnesium composite treatment, the [Ca] / [Als] ratio is controlled to be 0.102. Soft blowing argon lasts for 22 min.

[0062] 2. Continuous casting: Tundish superheat 22℃, casting speed 0.75m / min. Slab thickness 230mm, heavy reduction at the end of slab solidification, total reduction 22mm, and the center segregation index was measured to be 1.04.

[0063] 3. Rolling: The slab is heated to 1220℃ and held for 70 minutes. A multi-directional deformation rolling process is adopted. In the first step of rolling in the recrystallization zone, the side pressure of the vertical roll is 32%. In the second step of rolling in the non-recrystallization zone, the reversing rolling deformation rate is 13%. The remaining deformation is completed in the third step. The final rolling temperature is 825℃, and the cumulative total reduction rate is 79%.

[0064] 4. Three-stage gradient cooling: The first stage rapidly cools the steel plate surface to 600℃ at a cooling rate of 32℃ / s, the second stage air cools for 50s, the third stage cools the entire steel plate to 455℃ at a cooling rate of 8℃ / s, and finally air cools to room temperature.

[0065] The performance test results of the steel plate produced in this embodiment are as follows: Mechanical properties: Yield strength 565MPa, tensile strength 705MPa, elongation 20%.

[0066] Low temperature toughness: Transverse impact energy at -40℃ is 195J (average value), and thickness direction (Z direction) impact energy at -40℃ is 70J.

[0067] Z-direction performance: Z-direction reduction of area 40%.

[0068] Welding performance: After welding thermal simulation with a heat input of 300 kJ / cm, the impact energy of HAZ at -40℃ is 105 J.

[0069] Uniformity of performance in the thickness direction: Impact energy at -40℃ at 1 / 4 of the plate thickness is 205J, and impact energy at -40℃ in the core is 188J, with a difference of 17J.

[0070] Comparative example: A 100mm thick 460MPa grade steel plate was produced using conventional processes. The chemical composition of the steel was similar to that of the steel plate described in this invention, but it was not subjected to calcium-magnesium composite treatment and was produced using conventional rolling and cooling processes. The Z-direction reduction of area of ​​the finished steel plate was only 28%, and the impact energy of the 400kJ / cm thermal simulation HAZ-40℃ was 65J. Moreover, the impact energy of the core was more than 40J lower than that of the surface layer.

[0071] Conclusion: All performance indicators of Examples 1-3 of the present invention are superior to those of the comparative examples, especially the Z-direction performance and weld HAZ toughness, which are significantly improved, and the thickness direction uniformity is good, which fully proves the technical advancement and effectiveness of the manufacturing method described in the present invention.

[0072] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-strength, high-toughness, lamellar tear-resistant extra-thick steel plate, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.04%–0.07%, Si: 0.10%–0.25%, Mn: 1.40%–1.70%, P≤0.008%, S≤0.0015%, Als: 0.020%–0.035%, Ti: 0.012%–0.020%, Cu: 0.25%–0.50%, Ni: 0.20%–0.40%, Nb: 0.025%–0.045%, V: 0.04%–0.08%, Mg: 0.0012%–0.0020%, B: 0.0010%–0.0020%; the balance is Fe and unavoidable impurities; carbon equivalent 0.28%≤Ceq≤0.47%, Ceq=C+Si / 24+Mn / 6+Ni / 40+Cr / 5+ Mo / 4+V / 14; Welding crack sensitivity index 0.1325%≤Pcm≤0.203%, Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

2. The high-strength, high-toughness, lamellar-tear-resistant extra-thick steel plate according to claim 1, characterized in that, The finished steel plate has a gradient structure that transitions from ultrafine bainite on the surface to acicular ferrite in the core.

3. A method for manufacturing a high-strength, high-toughness, lamellar-tear-resistant extra-thick steel plate as described in claim 1 or 2, characterized in that, Includes the following steps: 1) Converter smelting: The carbon content at the converter endpoint is controlled at 0.04% to 0.07%, and the tapping temperature is controlled at 1600℃ to 1630℃. Composite deoxidation and alloying are adopted during the tapping process to ensure that the steel composition meets the design requirements. 2) LF refining and calcium-magnesium composite treatment: The LF refining time is controlled at 30-45 min. In the later stage of refining, calcium-magnesium composite treatment is carried out, and the calcium-aluminum mass ratio Ca / Als is controlled within the range of 0.09-0.

11. Finally, soft argon blowing is carried out for ≥15 min. 3) Continuous casting: Fully protected casting is adopted; the superheat of the tundish is 15-22℃, and the casting speed is 0.7-1.0m / min; the thickness of the continuously cast slab is ≥230mm, and heavy pressure is used at the end of solidification, with a total reduction of 15-22mm and a reduction rate of 0.8-1.0mm / s; the center segregation index of the slab is controlled to be ≤1.

05. 4) Slab heating and multi-directional deformation rolling: The slab heating temperature is 1180~1220℃, and the holding time is calculated as 4~6 times the slab thickness. The slab thickness is in meters (m) and the holding time is in hours (h). The multi-directional deformation rolling process is adopted, as detailed below: Step 1: Recrystallization zone rolling, performing one pass of large-reduction vertical roll rolling on the center area of ​​the wide side of the slab, with the side pressure controlled at 25% to 35%; Step 2: Rolling in the non-recrystallization zone. Rotate the slab 90° and perform one transverse rolling pass, with the deformation rate controlled at 10% to 15%. Step 3: Complete the remaining deformation using conventional longitudinal rolling, with the final rolling temperature controlled at 810–850℃, and the cumulative total reduction rate ≥75%; 5) Three-stage gradient cooling: First stage: Rapidly cool the surface of the steel plate to 550-600℃ at a cooling rate of ≥25℃ / s; Second stage: Turn off the cooling water and air cool for 30-60 seconds; The third stage: Restart the cooling water and cool the steel plate as a whole to the target final cooling temperature of 450-480℃ at a cooling rate of 5-8℃ / s, and then air cool it to room temperature.

4. The method for manufacturing a high-strength, high-toughness, lamellar-tear-resistant extra-thick steel plate according to claim 3, characterized in that, In step 2), during the calcium-magnesium composite treatment, magnesium wire is first fed in for magnesium treatment to control the Mg content in the steel within the target range; then calcium-iron wire is fed in for calcium treatment.

5. The method for manufacturing a high-strength, high-toughness, lamellar-tear-resistant extra-thick steel plate according to claim 3, characterized in that, In step 2), the calcium-aluminum mass ratio Ca / Als is controlled within the range of 0.095 to 0.

105.

6. The method for manufacturing a high-strength, high-toughness, lamellar-tear-resistant extra-thick steel plate according to claim 3, characterized in that, In step 3), the solidification end of the continuously cast slab refers to the range of solid fraction of 0.7 to 0.

9.

7. The method for manufacturing a high-strength, high-toughness, lamellar-tear-resistant extra-thick steel plate according to claim 3, characterized in that, In step 4), the recrystallization zone rolling is carried out in a temperature range of ≥1050℃, and the non-recrystallization zone rolling is carried out in a temperature range of 850~900℃.